A previously undetected fault has been found along the Salton Sea in California, easing fears a swarm of 200 small earthquakes last week would trigger a larger quake on the southern San Andreas Fault.
The newly mapped Salton Trough Fault runs parallel to the San Andreas Fault, and Valerie Sahakian, a researcher with the U.S. Geological Survey and lead author of the study, told USA Today the Salton Trough was difficult to find because it appears to be underwater.
The findings were published Thursday in the journal Bulletin of the Seismological Society of America.
The study authors said the existence of the Salton Trough seems to explain why it has been so long since a quake has occurred on the San Andreas Fault. A major event hasn’t hit the San Andreas Fault in more than 300 years although research suggests a magnitude 7 temblor should hit every 175 to 200 years.
"Based on the deformation patterns, this new fault has accommodated some of the strain from the larger San Andreas system, so without having a record of past earthquakes from this new fault, it's really difficult to determine whether this fault interacts with the southern San Andreas Fault at depth or in time," Nevada State Seismologist Graham Kent, one of the co-authors of the study and former researcher at the Scripps Institution of Oceanography at the University of California San Diego, said in a press release.
The biggest quake in last week’s swarm registered magnitude 4.3. Two smaller quakes struck Wednesday south of the swarm.
Scientists at Caltech in Pasadena, California, have found earthquakes occur much deeper in the Earth than previously believed.
Data from 5,000 state-of-the-art sensors installed atop the Newport-Inglewood Fault at Long Beach, California, and collected during a six-month period indicated quakes may occur 15 miles down, below the Earth’s crust and into the mantle where rock is so hot, it moves like hard honey, the Los Angeles Times reported. The fault is among the most dangerous in the Los Angeles Basin.
Caltech seismology professor Jean Paul Ampuero, one of the authors of the study published Thursday in the journal Science, said scientists didn’t think it was possible for a fault to extend that far down. He said the research indicates the San Andreas and other faults could experience earthquakes even more powerful than expected.
The studied earthquakes — actually microquakes no stronger than magnitude 2 —were so far down, they were not felt on the surface. The study indicates an earthquake occurring higher up could reach much further down, producing more damage and a possible rupture.
“That got us thinking — that if earthquakes want to get big, one way of achieving that is by penetrating deep,” Ampuero told the Times. “The big question is: If the next, larger earthquake happens, it manages to penetrate deeper than we think, it may be bigger than we expect.”
Current predictions along the Newport-Inglewood Fault are for a large earthquake ranging from 6 to 7.4 on the open-ended Richter scale.
The good news, Ampuero said, is these deep quakes don’t make surface quakes stronger. Also, the microquakes were sensed only beneath Long Beach. A four-week sample further north did not detect any activity.